Laughter may be the best medicine, but for some, it's nothing less than a disorder - a sleep disorder called narcolepsy can send a person into an instant slumber without warning if you laugh.
People with this order suffer temporary muscle weakness when they experience emotions such as surprise, fear and the exhilaration that comes from a good belly laugh.
It usually manifests itself as cataplexy, in which wide-awake sufferers "flop" as if falling into a deep sleep, reports The Daily Express.
"I lost strength in my hands or my head went limp and nodded forward for a few seconds when I laughed," said Claire Allen, who suffers from the disorder.
Claire, from Cambridge, was sometimes collapsing 100 times a day.
The majority of sufferers start experiencing it in their teens or early 20s when the combination of daytime fatigue and night-time insomnia is simply dismissed as adolescent laziness.
"Quality of life can be badly hit if untreated. Their studies suffer. They avoid driving. They are afraid to look after young children on their own and take baths. They don't get into relationships, get promoted or do physical exercise," said Dr John Shneerson, an expert at Papworth Hospital's sleep centre in Cambridge.
Shneerson says it is important for narcoleptics to keep to regular routines and take short naps. He added that it can be helped with the right kind of medication.